1. Field of the Invention
The present invention relates to an acoustic lens, a method for producing the same, an ultrasound probe having the acoustic lens, and an ultrasound imaging apparatus.
2. Description of Related Art
Ultrasound imaging apparatuses which use ultrasound for testing transmit ultrasound to a test subject (e.g., living organism) and receive a reflection wave (echo) of this ultrasound to thereby visualize the inside of the test subject for testing.
In an ultrasound imaging apparatus, an acoustic lens for an ultrasound probe is used in close contact with a test subject, and thus is required to have properties as mentioned below. From the viewpoint of suppressing the reflection (multiple reflection) of ultrasound between the acoustic lens and the test subject, the acoustic impedance of the acoustic lens is required to be close to that of the test subject. Further, from the viewpoint of high sensitivity, the attenuation factor of sound in the acoustic lens is required to be low. Furthermore, from the viewpoint of adaptation to various shapes of the acoustic lens, the moldability of the acoustic lens is required to be high. Thus, acoustic lenses for satisfying these requirements have been proposed (e.g., Japanese Patent Application Laid-Open No. 2011-072702 and Japanese Patent Application Laid-Open No. 2009-072605).
The acoustic lens disclosed in Japanese Patent Application Laid-Open No. 2011-072702 contains silicone rubber and metal oxide particles coated with silica. In this acoustic lens, the use of fine metal oxide particles having an average particle diameter of 30 nm may reduce the attenuation factor of sound.
The acoustic lens disclosed in Japanese Patent Application Laid-Open No. 2009-072605 contains silicone rubber and metal oxide particles. In this acoustic lens, the use of high-density zinc oxide, platinum oxide or ytterbium oxide as metal oxide particles may reduce the attenuation factor of sound.
In the acoustic lens disclosed in Japanese Patent Application Laid-Open No. 2011-072702, however, 10 to 60 parts by mass of metal oxide particles are required when the acoustic impedance is tried to be close to that of the test subject. Further, in the acoustic lens disclosed in Japanese Patent Application Laid-Open No. 2009-072605, 15 to 60 parts by mass of zinc oxide, 10 to 52 parts by mass of platinum oxide, or 12 to 56 parts by mass of ytterbium oxide is required, when the acoustic impedance is tried to be close to that of the test subject. Thus, in the acoustic lenses disclosed in the above-mentioned patent literatures, it is required to mix large amounts of metal oxide particles in order to obtain desired acoustic properties. However, when large amounts of metal oxide particles are mixed into silicone rubber, the metal oxide particles cannot be mixed into silicone rubber uniformly and stably. That is, the mixing property between metal oxide particles and silicone rubber becomes low. When the mixing property between metal oxide particles and silicone rubber thus becomes low, there is a concern that streak-shaped crystal defect (hereinafter, also referred to as “failure”) may undesirably occur in forming the acoustic lens. Accordingly the acoustic lenses disclosed in the above-mentioned patent literatures have room for improvement with regard to the mixing property between metal oxide particles and silicone rubber.